Drilling rigs operating in offshore oil fields are periodically exposed to environmental conditions, which to a high degree obstruct work. While drilling, new pipes must continously be added, and on the occations when the drillcrown must be changed all pipes in the drill-string must be pulled up and then reinstalled, when the new drill-crown has been fitted.
The various pipes used have about the same length, but several different diameters are required, because the diameter of the drill-hole varies from the first part, and then step-by-step gets smaller while the hole penetrates deeper.
For this operation casing tubes are used which protect the drill hole and remain therein, while the drill pipes may have to be removed and reinserted several times. Furthermore there is at least one marine riser line including a telescopic part, which is substantially thicker and longer than the drill pipes.
All these items require a large storage and handling area, which especially during winter and in arctic conditions means big difficulties during the moving of pipes between the storage area and the drill deck. For providing a weather-sheltered work area the work is performed upon two decks, wherein the upper deck comprises tunnels and a protecting enclosure around the derrick.